This invention relates to motion snubbing devices which are mounted between a supported body, such as a piping system, and a supporting body, such as buildings, for supporting piping systems in chemical plants, atomic power plants and so forth, so as to permit stable, low acceleration displacements between said supporting body and said supported body while restricting high acceleration displacements caused by sudden external forces.
Devices of this type are intended to permit the pipings to move slowly due to changes of temperature or the like, i.e, low acceleration displacements. They are further intended to support pipings in a stable manner over a long period of time, thus preventing damage to or rupture of the pipings by limiting the effects of any sudden external force. This is achieved by the braking operation of the interior of the devices in case of possible high acceleration displacements, i.e., displacements in excess of a threshold acceleration such as might be produced by earthquakes or the like.
Devices of this sort are generally called mechanical snubbers or arrestors and several types are well known. For example, U.S. Pat. Nos. 2,838,137, 3,809,186 and U.S. Pat. No. Re. 29,221 disclose this sort of device.
Devices of the type to which this invention pertains comprise a flexible member fixed on a rotary shaft and having a brake shoe, an inertia mass rotatably provided on the shaft in opposition to the member, and a frictional wall for braking-engagement with the brake shoe. Both the flexible member and the inertia mass are permitted to rotate together in a low acceleration range, but upon the occurrence of high accelerating displacements, the devices initiate a braking operation by engaging the brake shoe with the frictional wall due to the delayed motion of the inertia mass when it no longer rotates together with the flexible member. For example, U.S. Pat. No. 4,346,793 discloses this sort of device.
In devices of this type the inertia mass is rotatable on the shaft so that the brake operation surface is not restrained after high acceleration displacements have triggered the braking operation, even when a sudden external force is sequentially exerted in the course of the braking operation. That is, after a lag of operation of the inertia mass actuates the braking operation, the inertia mass rotates so that the braking operation is released, and this cycle is repeated so long as the external force continues to act thereon, thus preventing locking and damage to the devices. This is called the "self-release" function of the braking operation.
The conventional devices are constructed such that the inertia mass can rotate freely around the rotary shaft but is rigid in the axial direction. An impactive engagement of the brake shoe with the frictional surface may damage components of the device and bring about counteraction in the braking surface, thus lowering braking efficiency. Conventionally, it is difficult to adjust for irregularities in the finished devices because of rigid clearance between the brake shoe and the frictonal wall and in the positional adjustment of the worn frictional surface.